How do vaccines and immune systems work, and why could a coronavirus vaccine fail?

Anticipation is running high as scientists around the world race to develop a vaccine for Covid-19. Some vaccines showed very promising results in early data. But a vaccine is a highly complicated drug that works on the human body’s complex immune system. We will walk you through the issues to explain how the drug and the human body work, and why a vaccine may not work at all.What is the immune system? It is a complex system of cells, organs and processes that detect foreign substances,…

from South China Morning Post https://www.scmp.com/news/china/society/article/3096808/how-do-vaccines-and-immune-systems-work-and-why-could